Good luck Jaz, whatever you do. I would be gritting my teeth here if you insisted on losing it all so quickly, when it took years to put on, lol! And the BMI thing, OK, you want to be under 25, and I was keen to drop below 30 for my diving (for me, 25 is the next phase). I have now gone slightly over 30, but it's no big deal, and I have my diving medical, and know I can knock that off with ease on the next fast.
Rome was not built in a day, and if it was, it wouldn't look so nice!!